Steel for metal-cutting tools

ABSTRACT

A steel for metal-cutting tools comprising carbon, chromium, molybdenum, vanadium, aluminum and nitrogen in certain concentration ranges. This Abstract is not intended to define the invention disclosed in the specification, nor intended to limit the scope of the invention in any way.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 of Austrian Patent Application No. A 965/2003, filed on Jun. 23, 2003, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a steel for metal-cutting tools.

2. Discussion of Background Information

Cutting areas of tools are essentially highly stressed thermally, abrasively and in terms of toughness and compressive stress during a metal cutting of workpieces, and the stressing of the workpiece material takes place simultaneously. Alloy compositions which that take into account the highest demands in the stress profile to achieve the longest service life of the tool are known.

High wear resistance of a tool can be achieved in general with the use of high-speed steels, but these have high contents of the expensive alloying element(s) molybdenum and/or tungsten in concentrations up to 20% by weight. Vanadium also ranks as one of these elements and is added in concentrations of 1.2 to 10.0% by weight in conventional or PM (powder metallurgy) high-speed steels.

As set forth above, the compositions of high-speed steels can be selected for a required stress profile of the tool, but these steels have the disadvantage of high alloying costs and therefore high material costs. If the concentrations of the main alloying elements are reduced for reasons of economy, the heat-treatable quality, the hardness and the general performance characteristics of the steel may deteriorate abruptly.

It would be desirable to eliminate the deficiencies of the prior art steels and to provide a steel that is particularly suitable for metal-cutting tools and very cost-effective due to the alloying technique.

SUMMARY OF THE INVENTION

The present invention provides a steel for metal-cutting tools which comprises, in % by weight: C from about 0.88 to about 1.12 Cr from about 3.4 to about 4.5 Mo from about 2.5 to about 3.0 V from about 0.7 to about 1.0 Al from about 0.04 to about 0.1 N from about 0.02 to about 0.12 Si from 0 to about 0.42 Mn from 0 to about 0.44 S from 0 to about 0.3 the balance being Fe and accompanying and contaminating elements, provided that up to about 0.45% by weight of V may be replaced by an equal concentration of Nb.

Unless stated otherwise, in the present specification and in the appended claims the indicated weight percentages are based on the total weight of the steel composition.

In one aspect, the steel of the present invention may comprise at least one and, preferably, all of the following elements in the following concentration ranges. C from about 0.93 to about 1.07 Si from about 0.15 to about 0.42 Mn from about 0.15 to about 0.44 S from about 0.001 to about 0.3 Al from about 0.05 to about 0.07 N from about 0.03 to about 0.1.

In another aspect, the steel of the present invention preferably comprises less than 0.03% by weight of phosphorus.

In yet another aspect, the weight ratio of aluminum to nitrogen (Al/N) in the steel of the present invention may be from about 0.5 to about 1.9.

In a still further aspect, the steel of the present invention preferably comprises, in % by weight: C about 0.96 Cr about 4.01 Mo about 2.78 V about 0.88 Al about 0.082 N about 0.086 Si about 0.27 Mn about 0.24 S about 0.009.

The present invention also provides a metal cutting tool which comprises the steel of the present invention, including the various aspects thereof. For example, the metal cutting tool may comprise a saw blade such as e.g., a circular saw blade.

In one aspect, the saw blade may comprise teeth which have a hardness (HRC=Rockwell Hardness C) of greater than about 63, preferably greater than about 64 in at least the tip area thereof.

As set forth above, the present invention provides a steel for metal cutting tools which comprises, in % by weight, C from about 0.88 to about 1.12 Cr from about 3.4 to about 4.5 Mo from about 2.5 to about 3.0 V from about 0.7 to about 1.0 Al from about 0.04 to about 0.1 N from about 0.02 to about 0.12 the balance being Fe and accompanying and contaminating elements.

Advantages achieved with the invention may include that a favorable hot hardness and, in particular, a high wear resistance with adequate toughness and compressive stress resistance of the heat-treated steel can be achieved by a combination of the elements molybdenum and vanadium on the one hand, in a considerably reduced concentration compared with high-speed steel, and with aluminum and nitrogen contents on the other hand, in relatively high contents compared to the prior art. Metal-cutting tools made of the alloy according to the invention can be produced cost-effectively due to the low contents of expensive alloying elements, but they also have high stability in the stress profile, particularly for exceptional requirements.

It has been found that the flow of chips on the face or in the area after the cutting edge of a tool made from the steel according to the invention takes place in a more favorable manner and there are comparatively far fewer craters. The reason for this has not yet been scientifically explained, but without wishing to be bound to any theory, it is assumed that it may be due to a synergistic effect of the elements aluminum, nitrogen, carbon and vanadium. The high affinity of vanadium toward carbon and nitrogen which on the one hand advantageously affords a high hot hardness with the formation of very fine, homogenously distributed carbides and carbonitrides during heat-treatment, can on the other hand leave an adequate amount of reactive aluminum in the matrix. Under temperature stress, the aluminum forms an alumina surface layer through oxidation in the cutting area of the tool, which alumina acts like a coating which promotes the flow of chips. Aluminum in the matrix has also proven to promote a hot hardness and retention of hardness of the material according to the invention.

Vanadium can be partially replaced in the alloy by up to 0.45% by weight by niobium; however, in these cases the carbon content should preferably be set in the lower range of the indicated concentration range.

In a preferred aspect, the steel according to the present invention contains one or more of the elements in the following concentration range(s) in % by weight: C from about 0.93 to about 1.07 Si from about 0.15 to about 0.42 Mn from about 0.15 to about 0.44 P from 0 to about 0.03 S from about 0.001 to about 0.3 Al = from about 0.05 to about 0.07 N = from about 0.03 to about 0.1.

The particularly important areas in the property profile of the tool can be further increased by an intermixing of the provided concentration ranges of the elements in the alloy.

When the ratio of aluminum to nitrogen is from about 0.5 to about 1.9 (Al/N=about 0.5 to about 1.9), the material according to the invention has a high hot hardness and toughness in the heat-treated state or after a hardening and at least a single tempering operation in the range from about 450° C. to about 500° C., whereby the cutting wear on the tool is extremely low.

Circular saws with a hardness of greater than about 63 HRC, preferably greater than about 64 HRC, can be produced from a steel according to the invention with particular cost-effectiveness and with a long service life in heavy operation.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

An exemplary embodiment of the invention which shows only one embodiment of the steel of the present invention in comparison to a conventionally used material according to DIN No. 1.3343 is described in more detail below:

Circular saw blades with heat-treated teeth with a diameter of 400 mm were fixed on a common shaft and strong metal rods were thereby cut into pieces in the cutting device.

A saw blade of an alloy according to the invention labeled Exp. L. 3 was inserted between the saw blades of an alloy that has proven to be favorable with regard to the life of the saw blade and is labeled Type A 1 in Table 1.

Until the saw shaft was discarded due to wear, comparative evaluations were made in Table 2, the results of which are shown in Table 2, whereby the values of Type Al are given as 100%. The results show that high cutting capacities can be achieved for metal-cutting tools, in particular for circular saws, when using a material according to the invention. TABLE 1 Chemical Composition Material C Si Mn P S Cr Mo V W Al N Type A1 0.91 0.32 0.4 0.011 0.012 4.13 5.21 1.81 6.44 — — Exp.L.3 0.96 0.27 0.24 0.01 0.009 4.01 2.78 0.88 — 0.082 0.086

TABLE 2 Use Hardness Cutting Cutting Material Time % HRC Wear % Crater Wear % Breakage % Type A1 0 65 — — — Exp.L.3 0 64 — — — Type A1 30 — 100 100 100 Exp.L.3 30 — 103  95 100 Type A1 60 — 100 100 100 Exp.L.3 60 — 107  89 200 Type A1 90 — 100 100 100 Exp.L.3 90 — 106  86 100

It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 

1. A steel for metal-cutting tools, comprising in % by weight: C from about 0.88 to about 1.12 Cr from about 3.4 to about 4.5 Mo from about 2.5 to about 3.0 V from about 0.7 to about 1.0 Al from about 0.04 to about 0.1 N from about 0.02 to about 0.12 Si from 0 to about 0.42 Mn from 0 to about 0.44 S from 0 to about 0.3

the balance being Fe and accompanying and contaminating elements, provided that up to about 0.45% by weight of V may be replaced by an equal concentration of Nb.
 2. The steel of claim 1, wherein the steel comprises one or more elements in the following concentrations in % by weight: C from about 0.93 to about 1.07 Si from about 0.15 to about 0.42 Mn from about 0.15 to about 0.44 S from about 0.001 to about 0.3 Al from about 0.05 to about 0.07 N from about 0.03 to about 0.1.


3. The steel of claim 1, wherein the steel comprises in % by weight: C from about 0.93 to about 1.07 Si from about 0.15 to about 0.42 Mn from about 0.15 to about 0.44 S from about 0.001 to about 0.3 Al from about 0.05 to about 0.07 N from about 0.03 to about 0.1.


4. The steel of claim 1, wherein the steel comprises not more than about 0.03% by weight of P.
 5. The steel of claim 2, wherein the steel comprises not more than about 0.03% by weight of P.
 6. The steel of claim 1, wherein the ratio of aluminum to nitrogen (Al/N) is from about 0.5 to about 1.9.
 7. The steel of claim 2, wherein the ratio of aluminum to nitrogen (Al/N) is from about 0.5 to about 1.9.
 8. The steel of claim 3, wherein the ratio of aluminum to nitrogen (Al/N) is from about 0.5 to about 1.9.
 9. The steel of claim 1, comprising in % by weight: C about 0.96 Cr about 4.01 Mo about 2.78 V about 0.88 Al about 0.082 N about 0.086 Si about 0.27 Mn about 0.24 S about 0.009.


10. A metal cutting tool comprising the steel of claim
 1. 11. A metal cutting tool comprising the steel of claim
 2. 12. A metal cutting tool comprising the steel of claim
 3. 13. A metal cutting tool comprising the steel of claim
 9. 14. A saw blade comprising the steel of claim
 1. 15. A saw blade comprising the steel of claim
 2. 16. The saw blade of claim 14, wherein the saw blade comprises teeth and the teeth have a hardness (HRC) of greater than about 63 in at least a teeth tip area thereof.
 17. The saw blade of claim 15, wherein the saw blade comprises teeth and the teeth have a hardness (HRC) of greater than about 63 in at least a teeth tip area thereof.
 18. The saw blade of claim 14, wherein the saw blade comprises teeth and the teeth have a hardness (HRC) of greater than about 64 in at least a teeth tip area thereof.
 19. The saw blade of claim 15, wherein the saw blade comprises teeth and the teeth have a hardness (HRC) of greater than about 64 in at least a teeth tip area thereof.
 20. The saw blade of claim 14, wherein the saw blade comprises a circular saw blade. 